linux-ext4 - Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts

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Date:   Wed, 17 Jun 2020 18:44:29 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Masayoshi Mizuma <msys.mizuma@...il.com>
Cc:     "J. Bruce Fields" <bfields@...ldses.org>,
        Eric Sandeen <sandeen@...deen.net>,
        Christoph Hellwig <hch@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs <linux-xfs@...r.kernel.org>
Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts

On Wed, Jun 17, 2020 at 09:30:26PM -0400, Masayoshi Mizuma wrote:
> On Wed, Jun 17, 2020 at 02:45:07PM -0400, J. Bruce Fields wrote:
> > On Wed, Jun 17, 2020 at 01:28:11PM -0500, Eric Sandeen wrote:
> > > but mount(8) has already exposed this interface:
> > > 
> > >        iversion
> > >               Every time the inode is modified, the i_version field will be incremented.
> > > 
> > >        noiversion
> > >               Do not increment the i_version inode field.
> > > 
> > > so now what?
> > 
> > It's not like anyone's actually depending on i_version *not* being
> > incremented.  (Can you even observe it from userspace other than over
> > NFS?)
> > 
> > So, just silently turn on the "iversion" behavior and ignore noiversion,
> > and I doubt you're going to break any real application.
> 
> I suppose it's probably good to remain the options for user compatibility,
> however, it seems that iversion and noiversiont are useful for
> only ext4.
> How about moving iversion and noiversion description on mount(8)
> to ext4 specific option?
> 
> And fixing the remount issue for XFS (maybe btrfs has the same
> issue as well)?
> For XFS like as:
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 379cbff438bc..2ddd634cfb0b 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1748,6 +1748,9 @@ xfs_fc_reconfigure(
>                         return error;
>         }
> 
> +       if (XFS_SB_VERSION_NUM(&mp->m_sb) == XFS_SB_VERSION_5)
> +               mp->m_super->s_flags |= SB_I_VERSION;
> +

I wonder, does this have to be done at the top of this function because
the vfs already removed S_I_VERSION from s_flags?

--D

>         return 0;
>  }
> 
> Thanks,
> Masa